In an optical communications network, a known packaged optoelectronic module such as a transmitter, receiver or transceiver module typically comprises a housing containing an optical subassembly comprising, for example, an optoelectronic package having an optical connector for coupling to an external optical fibre for propagation of electromagnetic radiation to/from the network. The optoelectronic package has a laser device or a photodetector therein, and an array of flexible leads for communicating electrical signals to and from the interior of the optoelectronic package. The array of flexible conducting leads is typically coupled to a Printed Circuit Board (PCB) comprising known circuitry suitable for controlling the laser device or photodetector and to provide functionality to the module.
In order to provide efficient coupling of electromagnetic radiation between the optical connector and an optoelectronic device located within the optoelectronic package, such as the laser device or the photodetector, an initial alignment process is necessary between the optical connector and active region of the optoelectronic device, for example a light emitting portion of the laser device in the case of the transmitter module or an absorbing portion of the photodetector in the case of the receiver module, or both for a tranceiver module. For an ideal coupling between the optical connector and the optoelectronic package, a central longitudinal axis associated with the optical connector should coincide with a centrally located axis passing through a wall of the optoelectronic package. However, the above initial alignment process typically results in the optical subassembly having an axial misalignment between the longitudinal axis of the optical connector and the central axis of the optoelectronic package. The amount of axial misalignment also varies between individual optical subassemblies according to the degree of positional adjustment of the optical connector necessary to align the optical connector with the optoelectronic device during the initial alignment process. Typically, the optical connector forms part of an industry standard connector, for example, a Lucent® Connector (LC) having a socket opening having a pre-defined configuration for receiving a complementarily shaped plug, the optical connector lying within the socket. The socket opening is integrally formed with the housing, the optical connector being fixed within the socket opening so as to maintain a fixed positional relationship between the socket opening and the optical connector. The inconsistent axial alignment between the individual optical connectors and the optoelectronic packages also results in the positional relationship between the optoelectronic packages and the PCBs varying from module to module. This inconsistent positional relationship between the optoelectronic packages and the PCBs complicates the design of a generic packaged optoelectronic module.
In order to accommodate the variations in the positional relationship between the optoelectronic packages and the PCBs, it is known for the length of the array of flexible leads to vary in order to, where appropriate, bridge an increased wiring path between the optoelectronic packages and the PCBs. However, such an increase in electrical paths can result in an increase in undesirable capacitive effects experienced by electrical signals using the extended array of leads.
Additionally, where the laser diodes are housed within the optoelectronic packages, it is necessary to sink heat generated by the laser diodes. In addition to the relative position between the optoelectronic packages and the PCBs being inconsistent, the positional relationships between bases of the optoelectronic packages and housings containing the optoelectronic packages are also inconsistent, resulting in an inability to thermally couple the bases of the optoelectronic packages with the housings of the optoelectronic modules in order to provide efficient heat removal from the optoelectronic package while in operation; efficient heat removal requires that the source of the heat dissipation, for example the optoelectronic package comprising the semiconductor laser device, to be disposed in intimate contact with the housing or other means of heat removal. Due to the inconsistent positional relationship between the bases of the optoelectronic packages and the housings, a variable gap typically exists between the housings and the optoelectronic packages.
Without an efficient means of heat removal, the ambient temperature inside the packaged optoelectronic module can rise above the rated range of thermal operability recommended for components disposed upon the PCB and the optoelectronic device within the optoelectronic package, which can lead to malfunctions in the circuitry of the PCB and/or an unwanted variability in the laser device output characteristics or photodetector efficiency.